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Newton's First Law = Inertia

8.1 - An objectís inertia causes it to continue moving the way it is moving unless it is acted upon by an (unbalanced) force to change its motion. An unbalanced force is a net force.

"Every object remains in a state of rest or of uniform motion in a straight line unless acted upon by an outside force." (An outside force is a net force.)

Inertia is the resistance to changes in motion. Inertia is proportional to mass. Big masses resist changing their motion more than smaller masses.

Objects at rest remain at rest unless acted on by a net force.

[train]

[baby stoller]

A lot of inertia! The large train resists changing its motion.

Very little inertia. The small baby carriage has very little resistance to changes in motion.

Since the train is so huge, it is difficult to change its speed. In fact, a large net force is required to change its speed or direction.

Since the baby carriage is so small, it is very easy to change its speed or direction. A small net force is required to change its speed or direction.

 

Objects in motion remain in motion in a straight line (unless acted upon by an outside force).

[train]

[soccer ball]

A lot of inertia!

Very little inertia

Since the train is so huge, it is difficult to stop it once it is moving. It is difficult to change its speed. In fact, a large net force is required to change its speed.

Since the soccer ball is so small, it is very easy to stop it once it is moving. A small net force is required to change its speed.

 

What is the difference between inertia and momentum?

Inertia is proportional to mass. It is a measure of the resistance to changes in velocity.

Momentum = mass x velocity

Inertia is a property of mass and cannot change. Momentum changes as an object changes its velocity.

 

 

Some other types of inertia:

Gyroscopic Inertia = "A body that is set spinning has a tendency to keep spinning in its original orientation."

For example, a top or gyroscope will not fall over when it is spinning.

 

Rotational Inertia = the property of an object that resists any change in its state of rotation. If at rest, it tends to remain at rest; if rotating, it tends to remain rotating and will continue to do so unless interrupted. For example, think of a metal ring and a solid disk experiment. The metal ring has its mass at the perimeter and therefore has more rotational inertia than the solid disk. This is why a ring resists rolling from a state of rest.   

 

 

 

 

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